2.1. Field of the Technology
The present technology relates to the determining of sleep stage of humans such as using respiration and movement signals and may be useful, for example, in the assessment of sleep architecture or the quality of sleep. The technology may be implemented in conjunction with devices for the diagnosis, treatment and amelioration of respiratory disorders, and to procedures to prevent respiratory disorders. Thus, the present technology may relate to medical devices, and their use for treating respiratory disorders and for preventing respiratory disorders.
2.2. Description of the Related Art
The respiratory system of the body facilitates gas exchange. The nose and mouth form the entrance to the airways of a patient.
The airways include a series of branching tubes, which become narrower, shorter and more numerous as they penetrate deeper into the lung. The prime function of the lung is gas exchange, allowing oxygen to move from the air into the venous blood and carbon dioxide to move out. The trachea divides into right and left main bronchi, which further divide eventually into terminal bronchioles. The bronchi make up the conducting airways, and do not take part in gas exchange. Further divisions of the airways lead to the respiratory bronchioles, and eventually to the alveoli. The alveolated region of the lung is where the gas exchange takes place, and is referred to as the respiratory zone. See West, Respiratory Physiology—the essentials.
A range of respiratory disorders exist.
Obstructive Sleep Apnea (OSA), a form of Sleep Disordered Breathing (SDB), is characterized by occlusion or obstruction of the upper air passage during sleep. It results from a combination of an abnormally small upper airway and the normal loss of muscle tone in the region of the tongue, soft palate and posterior oropharyngeal wall during sleep. The condition causes the affected patient to stop breathing for periods typically of 30 to 120 seconds duration, sometimes 200 to 300 times per night. It often causes excessive daytime somnolence, and it may cause cardiovascular disease and brain damage. The syndrome is a common disorder, particularly in middle aged overweight males, although a person affected may have no awareness of the problem. See U.S. Pat. No. 4,944,310 (Sullivan).
Cheyne-Stokes Respiration (CSR) is a disorder of a patient's respiratory controller in which there are rhythmic alternating periods of waxing and waning ventilation, causing repetitive de-oxygenation and re-oxygenation of the arterial blood. It is possible that CSR is harmful because of the repetitive hypoxia. In some patients CSR is associated with repetitive arousal from sleep, which causes severe sleep disruption, increased sympathetic activity, and increased afterload. See U.S. Pat. No. 6,532,959 (Berthon-Jones).
Obesity Hyperventilation Syndrome (OHS) is defined as the combination of severe obesity and awake chronic hypercapnia, in the absence of other known causes for hypoventilation. Symptoms include dyspnea, morning headache and excessive daytime sleepiness.
Chronic Obstructive Pulmonary Disease (COPD) encompasses any of a group of lower airway diseases that have certain characteristics in common. These include increased resistance to air movement, extended expiratory phase of respiration, and loss of the normal elasticity of the lung. Examples of COPD are emphysema and chronic bronchitis. COPD is caused by chronic tobacco smoking (primary risk factor), occupational exposures, air pollution and genetic factors. Symptoms include: dyspnea on exertion, chronic cough and sputum production.
Neuromuscular Disease (NMD) is a broad term that encompasses many diseases and ailments that impair the functioning of the muscles either directly via intrinsic muscle pathology, or indirectly via nerve pathology. Some NMD patients are characterised by progressive muscular impairment leading to loss of ambulation, being wheelchair-bound, swallowing difficulties, respiratory muscle weakness and, eventually, death from respiratory failure. Neuromuscular disorders can be divided into rapidly progressive and slowly progressive: (i) Rapidly progressive disorders: Characterised by muscle impairment that worsens over months and results in death within a few years (e.g. Amyotrophic lateral sclerosis (ALS) and Duchenne muscular dystrophy (DMD) in teenagers); (ii) Variable or slowly progressive disorders: Characterised by muscle impairment that worsens over years and only mildly reduces life expectancy (e.g. Limb girdle, Facioscapulohumeral and Myotonic muscular dystrophy). Symptoms of respiratory failure in NMD include: increasing generalised weakness, dysphagia, dyspnea on exertion and at rest, fatigue, sleepiness, morning headache, and difficulties with concentration and mood changes.
Chest wall disorders are a group of thoracic deformities that result in inefficient coupling between the respiratory muscles and the thoracic cage. The disorders are usually characterised by a restrictive defect and share the potential of long term hypercapnic respiratory failure. Scoliosis and/or kyphoscoliosis may cause severe respiratory failure. Symptoms of respiratory failure include: dyspnea on exertion, peripheral oedema, orthopnea, repeated chest infections, morning headaches, fatigue, poor sleep quality and loss of appetite.
Otherwise healthy individuals may take advantage of systems and devices to prevent respiratory disorders from arising.
2.2.1 Systems
One known product used for treating sleep disordered breathing is the S9 Sleep Therapy System, manufactured by ResMed.
2.2.2 Therapy
Nasal Continuous Positive Airway Pressure (CPAP) therapy has been used to treat Obstructive Sleep Apnea (OSA). The hypothesis is that continuous positive airway pressure acts as a pneumatic splint and may prevent upper airway occlusion by pushing the soft palate and tongue forward and away from the posterior oropharyngeal wall.
Non-invasive ventilation (NIV) has been used to treat OHS, COPD, MD and Chest Wall disorders.
2.2.3 Patient Interface
The application of a supply of air at positive pressure to the entrance of the airways of a patient is facilitated by the use of a patient interface, such as a nasal mask, full-face mask or nasal pillows. A range of patient interface devices are known, however a number of them suffer from being one or more of obtrusive, aesthetically undesirable, poorly fitting, difficult to use and uncomfortable especially when worn for long periods of time or when a patient is unfamiliar with a system. Masks designed solely for aviators, as part of personal protection equipment or for the administration of anaesthetics may be tolerable for their original application, but nevertheless be undesirably uncomfortable to be worn for extended periods, for example, while sleeping.
2.2.3.1 Seal-Forming Portion
Patient interfaces typically include a seal-forming portion.
One type of seal-forming portion extends around the periphery of the patient interface, and is intended to seal against the user's face when force is applied to the patient interface with the seal-forming portion in confronting engagement with the user's face. The seal-forming portion may include an air or fluid filled cushion, or a moulded or formed surface of a resilient seal element made of an elastomer such as a rubber. With this type of seal-forming portion, if the fit is not adequate, there will be gaps between the seal-forming portion and the face, and additional force will be required to force the patient interface against the face in order to achieve a seal.
Another type of seal-forming portion incorporates a flap seal of thin material so positioned about the periphery of the mask so as to provide a self-sealing action against the face of the user when positive pressure is applied within the mask. Like the previous style of seal forming portion, if the match between the face and the mask is not good, additional force may be required to effect a seal, or the mask may leak. Furthermore, if the shape of the seal-forming portion does not match that of the patient, it may crease or buckle in use, giving rise to leaks.
Another form of seal-forming portion may use adhesive to effect a seal. Some patients may find it inconvenient to constantly apply and remove an adhesive to their face.
A range of patient interface seal-forming portion technologies are disclosed in the following patent applications, assigned to ResMed Limited: WO 1998/004,310; WO 2006/074,513; WO 2010/135,785.
2.2.3.2 Positioning and Stabilising
A seal-forming portion of a patient interface used for positive air pressure therapy is subject to the corresponding force of the air pressure to disrupt a seal. Thus a variety of techniques have been used to position the seal-forming portion, and to maintain it in sealing relation with the appropriate portion of the face.
One technique is the use of adhesives. See for example US Patent publication US 2010/0000534.
Another technique is the use of one or more straps and stabilising harnesses. Many such harnesses suffer from being one or more of ill-fitting, bulky, uncomfortable and awkward to use.
2.2.3.3 Vent Technologies
Some forms of patient interface systems may include a vent to allow the washout of exhaled carbon dioxide. Many such vents are noisy. Others may block in use and provide insufficient washout. Some vents may be disruptive of the sleep of a bed-partner 1100 of the patient 1000, e.g. through noise or focussed airflow.
ResMed Limited has developed a number of improved mask vent technologies. See WO 1998/034,665; WO 2000/078,381; U.S. Pat. No. 6,581,594; U.S. patent application; US 2009/0050156; US Patent Application 2009/0044808.
Table of noise of prior masks (ISO 17510-2:2007, 10 cmH2O pressure at 1 m)A-weightedA-weightedsound powersound pressurelevel dbAdbAYearMask nameMask type(uncertainty)(uncertainty)(approx.)Glue-on (*)nasal50.942.91981ResCarenasal31.523.51993standard (*)ResMednasal29.521.51998Mirage (*)ResMednasal36 (3)28 (3)2000UltraMirageResMednasal32 (3)24 (3)2002Mirage ActivaResMednasal30 (3)22 (3)2008Mirage MicroResMednasal29 (3)22 (3)2008Mirage SoftGelResMednasal26 (3)18 (3)2010Mirage FXResMednasal37 29 2004Mirage Swift (*)pillowsResMednasal28 (3)20 (3)2005Mirage Swift IIpillowsResMednasal25 (3)17 (3)2008Mirage Swift LTpillows(* one specimen only, measured using test method specified in ISO3744 in CPAP mode at 10 cmH2O)
Sound pressure values of a variety of objects are listed below
A-weightedsound pressure dbAObject(uncertainty)NotesVacuum cleaner: Nilfisk68ISO3744 at 1 mWalter Broadly Litter Hog: B+distanceGradeConversational speech601 m distanceAverage home50Quiet library40Quiet bedroom at night30Background in TV studio202.2.3.4 Nasal Pillow Technologies
One form of nasal pillow is found in the Adam Circuit manufactured by Puritan Bennett. Another nasal pillow, or nasal puff is the subject of U.S. Pat. No. 4,782,832 (Trimble et al.), assigned to Puritan-Bennett Corporation.
ResMed Limited has manufactured the following products that incorporate nasal pillows: SWIFT nasal pillows mask, SWIFT II nasal pillows mask, SWIFT LT nasal pillows mask, SWIFT FX nasal pillows mask and LIBERTY full-face mask. The following patent applications, assigned to ResMed Limited, describe nasal pillows masks: International Patent Application WO2004/073,778 (describing amongst other things aspects of ResMed SWIFT nasal pillows), US Patent Application 2009/0044808 (describing amongst other things aspects of ResMed SWIFT LT nasal pillows); International Patent Applications WO 2005/063,328 and WO 2006/130,903 (describing amongst other things aspects of ResMed LIBERTY full-face mask); International Patent Application WO 2009/052,560 (describing amongst other things aspects of ResMed SWIFT FX nasal pillows).
2.2.4 PAP Device
The air at positive pressure is typically supplied to the airway of a patient by a PAP device such as a motor-driven blower. The outlet of the blower is connected via a flexible delivery conduit to a patient interface as described above.
2.2.5 Sleep Detection
Sleep information may be useful for treating and/or diagnosing respiratory issues or may simply be useful for monitoring health. Currently, human sleep stages are typically determined using a laboratory based measurement called polysomnography. In polysomnography, it is typical for several electroencephalogram (EEG) readings to be taken (EEGs are the microvolt potentials generated by brain activity that can be measured at the scalp using electrodes), in addition to other parameters such as respiration, electrocardiogram (ECG), leg movements, and electro-oculograms (EOG). Based on work originally pioneered by Rechtschaffen and Kales (R&K), it is now conventional to score human sleep in 30-second epochs, and to label these epochs using sleep stage labels.
At present, the American Academy of Sleep Medicine defines the stages of sleep as:
Wake—this is when a person is fully awake, and is characterized by a positive dominant rhythm in the occipital EEG channel (when eyes are closed), typically in the range 8-14 Hz (often referred to as alpha waves)
Stage N1—this is the lightest stage of sleep, and is characterized by the appearance of some low amplitude waves at multiple frequencies interspersed with the alpha waves for >50% of an epoch. There may also be sharp vertex waves, some slow eye movements on the EOG and/or an overall lowering of the frequency of EEG.
Stage N2—this is a slightly deeper stage of sleep, and is marked by the appearance of sleep spindles and K-complexes, on a background of mixed frequency signals. Sleep spindles are bursts of higher frequency activity (e.g. >12 Hz). K-complexes are distinct isolated bipolar waves lasting about 1-2 seconds.
Stage N3 is the deepest stage of sleep (in the original R&K classification, there were two distinct stages called Stage 3 and Stage 4). This is characterised by the appearance of slow waves (e.g., 1-2 Hz frequency) for at least 20% of an epoch.
Stage R (REM)—this is rapid eye movement sleep, and is apparent through the presence of distinct activity in the EOG signal. The EEG signals recorded are typically quite similar to Stage N1 or even wake.
An automated system from scoring polysomnogram data is discussed in U.S. Pat. No. 5,732,696 to Rapoport et al. The system uses a computer to look for elemental patterns in the PSG data (such as the sleep spindles described above), and then uses a probabilistic weighting to score each epoch. However this approach to the problem of determining sleep stages is limited by the technical difficulty of measurement of a full set of polysomnogram signals, and hence is difficult and cumbersome to implement for more than a single night.
A number of systems have provided alternative solutions to the problem of determining sleep stage. One approach is to use actigraphy, in which small motion sensors (e.g., accelerometers) are worn by a user, typically in a wristwatch configuration. However, such systems have the disadvantage that they can only distinguish between sleep and wake, with poor accuracy in patients with sleep disorders.
US2006/0184056 (Heneghan et al) describes a sleep monitoring system which uses an ECG signal which is processed to determine a status for each epoch, either apneic or normal.
WO2007/143535 (Heneghan et al) describes a system for monitoring physiological signs such as sleep state by monitoring motion, breathing, and heart rate signals obtained in a non-contact fashion. A classifier model is applied to the streams of data.
A system which combines ECG and respiration methods to determine simplified sleep stage is described in US20090131803 (Heneghan et al). This combines signal characteristics derived from cardiogram and respiration signals, such as the amplitude modulation of the ECG signal and the dominant respiratory frequency in order to distinguish sleep from wakefulness.
WO2004112606 (Heneghan et al) describes a method of detecting sleep apnea using trans-cervical bioimpedance measurements.
US2011/0124979 (Heneghan et al) describes an approach to sleep monitoring using ECG and photoplethysmogram (PPG) data. These may be sensed using a Holter monitor and a pulse oximeter which are wearable in an ambulatory manner.
An approach in which cardiac R-R wave intervals are used to designate sleep as REM or non-REM is discussed in U.S. Pat. No. 5,280,791 to Lavie. A power spectrum of the cardiac R-R interval is calculated in order to determine the stages of sleep.
A US application 2013/0006124, to Eyal and Baharav, discusses the use of a non-ECG device such as a plethysmograph, radar, microphone, accelerometer etc., for measuring patient's heartbeats, analysing the inter-beat intervals and determining if the subject is in a sleep stage (light sleep, slow wave sleep, REM).